Pebble heater for liquid feed process



Oct. 16, 1956 c, BEARER PEBBLE HEATER FOR LIQUID FEED PROCESS Filed Jan. s, 1952 hired rates l, 2,767,130 Patented Oct. 16, 1956 PEBBLE HEATER FOR LIQUH) FEED PROCESS Louis C. Bearer, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Belaware Application January 3, 1952, Serial No. 264,7 77

19 Claims. (Cl. 19d-559 rIhis invention relates to a process and apparatus for eecting endotherrnic chemical reactions in liquid phase in a pebble heater type apparatus. A specific aspect of the invention relates to the cracking of liquid hydrocarbons in mixed liquid vapor phase in a modified pebble heater.

Pebble heat-exchange apparatus has been applied to a wide variety of processes where rapid heating of gases to high temperatures is desirable, including heating of air, nitrogen, steam, and gaseous reactants. In this type of operation, a continuons compact mass of highly refractory pebbles descends by gravity through a series of heatexchange chambers, absorbing heat from a hot gas, usually combustion gas, in an upper chamber and delivering the heat required for heating and/or chemical reaction in a lower chamber by direct contact with the feed gas therein.

When cracking or otherwise converting hydrocarbons to more desirable products in a pebble heater the feed is generally introduced into the reactor in vapor phase, being introduced at the bottom thereof and passing upwardly in countercurrent flow to the gravitating pebbles. A process ot' cracking liquid hydrocarbons in a pebble heater has been devised which entails atomizing or otherwise dispersing the hydrocarbon in liquid form into the top of the pebble heater reactor, thereby vaporizing a substantial portion of the feed immediately, the remaining liquid portion being deposited on the descending pebbles. This liquid unvaporized portion of the hydrocarbon passes downwardly through the reactor through a considerable portion thereof before being cracked or otherwise con- Verted to hydrocarbons vaporizable under the temperature conditions in the reactor. In this type of operation a considerable portion of the feed is laid down in the form of coke or tar on the pebbles. A troublesome disadvantage involved with this type of process wherein the liquid hydrocarbon is introduced into the top of the reactor is in the unduly high outlet pebble temperature from the reactor which necessitates another cooling chamber or the use of expensive high temperature alloys throughout the elevator equipment. in the latter case the heat loss from the pebble transfer equipment is unduly excessive and uneconomical. Another disadvantage accruing to the conventional liquid feed process is the requirement of a vapor seal such as steam in the pebble transfer equipment. No particular mechanical problems are involved in maintaining this type of seal but the expense involved is a factor in the cost of the products derived from the process.

The principal objective of the invention is to provide an improved process and apparatus for effecting endothermic chemical reactions in liquid phase and particularly for cracking heavy liquid hydrocarbons in liquid phase. It is also an object of the invention to increase the thermal eciency of a pebble heater in cracking heavy liquid hydrocarbons. Another object of the invention is to reduce pebble outlet temperature from the reaction Zone of a pebble heater. Other objects of the invention will become y apparent from a consideration of the accompanying disclosure.

The invention provides for the introduction of a heavy liquid hydrocarbon or other liquid feed requiring high temperature for reaction or conversion thereof into the elevator housing of a pebble heater system and maintaining the liquid level therein at such a level that the feed is forced through the pebble chute or conduit leading from the reaction chamber to the bottom of the elevator to the desired level in the reactor. This liquid level in the reactor can be maintained at practically any location intermediate the lower and upper sections of the reactor depending upon the type of conversion intended and the type of feed being processed. Ordinarily in the crackin of heavyr hydrocarbons the liquid level is maintained somewhere in the region between the midpoint of the reactor and the juncture of the top of the pebble mass with the sides of the reactor.

A more complete understanding of the invention may be obtained from a consideration of the drawing of which Figure l is an elevational view showing a diagrammatic arrangement of pebble heater apparatus adapted to the conversion of liquid feeds in a pebble heater. Figure 2 is au isometric View of one type of perforate elevator buoi-:et which is useful in the process.

Referring to Figure l, chamber 11 is a heavily insulated pebble heating chamber and chamber l2 is a similarly insulated reaction chamber connected to the former by an insulated throat 13 which extends into the reactor a short distance. A pebble inlet i4 in chamber il and a pebble outlet lo in chamber l2 provide for pebble ingress and egress from the heat-exchange portion of the pebble heater apparatus. Pebble heating chamber il is provided with a gas inlet line i7 and combustion gas outlet stack i8. Line i7 may carry either a combustible mixture of fuel and air or hot combustion gas directly from a furnace adjacent heater il or in an additional modification of the apparatus, i7 may represent a burner attached to the bottom of the heater and arranged to feed hot combastion gas directly into the same. in both the upper and lower heat-exchange chambers the pebbles are introduced thereto at a point below the top of the chambers so as to form a bed of pebbles having a generally conical top surface i9 and to provide a vapor collecting space 2l.

Pebble chutes 22 and 23 provide means for transferring pebbles to and from the elevator, respectively. Elevator 2d is of the bucket type and is provided with a continuous chain it', and perforate buckets Z7. These perforate buckets are designed to permit the drainage of liquid fee from the pebbles as they are elevated to the outlet chute Z3. Numeral l refers to a liquid-level-controller which 's in actuating communication with motor valve 29 in me ai. Any suitable type of liquid-level-controlier can e utilized in the arrangement of apparatus. Feed introuced through line 31 passes through the lower section of the elevator housing into pebble chute 22 and bypasses pebble feeder E@ in outlet conduit i6 by means of yp-ass conduit 32 provided with control valve 33. The upper end of conduit 32 is curved so that pebbles cannot enter and thereby hinder the ow of liquid feed into the reactor. Flow of pebbles out of the reactor is provided by conduit lo under the control of pebble feeder which may be oi any conventional type such as a star feeder. it is preferable that the vanes or other pebble motivating elements of the feeder be perforate so as to ahow a portion of the feed to pass upwardly through the feeder in countercurrent flow to the pebbles, thereby effecting a washing action on the pebbles and aiding in the prevention of agglomeration of pebbles. The feed passes upwardly through the reactor in liquid form countercurrently to the ow of pebbles until it reaches such a temperature point that vapori/tation and/or cracking and Y Y Y 3y volatilization take place. The gaseous products of the process are withdrawn through line 34. Lines 36, 37, 38, and 39 represent effluent lines positioned at different levels along the side of the reactor for withdrawing sidecuts of different composition resulting from varying degrees of cracking. The particular location of these lines andthe number of sidecuts withdrawn depend upon'the type of feed being processed and the reaction conditions being utilized. Y

Varying the liquid level in the reactor, of course, varies the vapor phase cracking space above the liquid level 20. Hence, it is feasible to withdraw products of varying compositions in vapor form from the withdrawal lines 36, 37, 38, and 39 when these lines are above the liquid levelr20. The higher the level of the 'withdrawal line, the greater the depth of cracking and the lighter the cut obtained from that line. More than one side-cut can be obtained at the same time in which case the lightest cut is recovered from eiliuent line 34, the next lightest from line 36, etc. It is also feasible with the apparatus shown to withdraw a liquid side-cut from any withdrawal Vline below the liquid level. Such a side-cut is advantageouslyA processed Vby fractionation to recover recycle stock and heavy bottoms for other uses or disposal.

Figure 2 shows one type of elevator bucket utilizable in the process. Perforations 42 serve to drain the liquid an'unobstructed pebble conduit 16 and vary the Vpebble feed from the pebbles and buckets as they pass from the liquid feed in the elevator housing upwardly to the delivery point at the top Vof the elevator.

The apparatus and process of the invention are particularlyapplicable to the cracking of heavy liquid hydrocarbon boiling above 500 F. and even hydrocarbon oil boiling above 900 F. Vacuum distillate and crude oil Vcan be processed to advantage in the apparatus disclosed.

The temperature of pebbles` entering the reactor may range from 1200 F. to 2400 F. depending upon the gravity of the'feed and the extent of conversion cr cracking desired. The gaseous eluent from the reaction when cracking heavy liquid hydrocarbons consists chiefly of oleiins, methane, and hydrogen. tinuously or intermittently draw olf a bottoms cut from an intermediate section of the reactor below the liquid level, e. g., through line 39.

The pebbles utilized in the process may be any of the conventional pebbles of the art. The term pebble as used throughout this specification denotes any solid refractory contact material, either catalytic or non-catalytic with respect to the process in which it is used, of dowable form and size, and suciently rugged and abrasive resistant for use in cyclic heat-exchange processes. Pebbles are preferably substantially spherical and relatively uniform in size in a given process, but may be of other shapes, either regular or irregular and non-uniform in slze. function desirably in pebble heat-exchange processes and those inthe range of 1A inch to 5/8 inch are most practical. Since pebble heat-exchange apparatus has its greatest utility in processes requiring gas heating and/or ret It is desirable to conilow rate by varying the elevator speed so as to eliminate pebble feeder 30.

The feed admitted through line 31 may be preheated but it is more desirable to introduce the feed into the elevator housing at normal or atmospheric temperature since a cooler feed aids in reducing the temperature ofV the pebbles being elevated in elevator 24. As theV feed passes downwardly through the elevator housinginto pebble chute 22 it continuously extracts heat from the pebbles and is heated thereby so that, as the feed enters v the bottom of reactor 12, it issuciently preheated that vaporization soon occurs with, subsequent cracking in vapor phase above the liquid level. It is quite apparent that the introduction of the cool feed in liquid' phase to the elevator housing aids greatly in extracting available heat from the pebbles so as to reduce the temperature thereof suiciently to avoid the usual problem'of transferring hot pebbles at unduly high temperatures and permits this transfer in ordinary cast iron elevator equipment. This feature of the process and apparatus is a further advantage in increasing the thermal eiciency of the process by considerably reducing heat losses. In the system described, the pebbles are at extremely high temperatures onlyrin the heater 11, connecting throat 13, and reactor 12, all of which are heavily insulated to prevent excessive heat loss. In conventional processes the heat losses in transfer conduits 22 and 23 and in the elevator are excessive due to the extremely high exit temperature of the pebbles, for example in the Vrange of 800 to l200 F. Y

It is further necessary to maintain the Yfeed level in the elevator slightly higherV than the desired liquid level in the reactor because of the pressure drop through the connecting conduit and pebble mass therein as well as the mass of pebbles in the reactor. v The diiference in liquid levels is determined by the Weight of the feed, the rate of pebble flow, and the reaction conditions in general. The exact level differential can be determined with little difficulty for each feed and set of reaction conditions.

vThe following specic examples are illustrative and provide a more complete understanding of the process and apparatus. Y

Example A heavy oil feed having the characteristics set forth .below is passed into the elevator'housing of pebble heater vaporiz'ed products are withdrawn from the vapor outlet Spheres of about 1A; inch to l inch in diameter pebbles have been compacted from alumina, mullite, Y

aluminamullite, zirconia, magnesia, beryllia, thoria, periclase, natural and synthetic clays, and mixtures of these materials. Spheres formed of high temperature alloys and metals have also been found practical in some proc- CSSSS.

Pebble ow is conveniently controlled by means of pebble feederV 30 so as to regulate the Vamount, of heat introduced to chamber 12. It is, of course, feasible to utilize constant pebble ow and vary the entering pebble temperature by changing'or regulating heating conditions in chamber 11 so as to increase and decrease the temperature to which the pebbles are heated. Another method and passed to a quench zone followed by separation of the products. A liquid stream is Withdrawn from the upper portion of the liquid-filled zone and fractionated in a conventional distillation column, not shown) to remove heavy bottoms.V (The lighter portion of this liquid stream may be recycled to the reactor.)

The followingV data represent the results obtained in such anroperation:

V Y, V Y Wt. percentbased on feed K GaseousV (C4 and lighter hydrocarbons and hy- 50.5 drogen; 78% unsaturated, mostly ethylene and propylene).

Gasoline (85 O. N. ASTM; 98.5 O. N. Re-V Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

l claim:

1. A process for cracking heavy liquid hydrocarbon in contact with a hot gravitating mass of pebbles which comprises gravitating a compact mass of pebbles successively through a series of enclosed contiguous zones, comprising a pebble heating zone, a relatively narrow connecting zone, and a hydrocarbon heating and cracking zone; gravitating said pebbles from the bottom of said heating and cracking zone through an enclosed lower pebble transfer zone to an enclosed pebble elevator zone; elevating said pebbles to an upper enclosed pebble transfer zone above the upper end of said pebble heating zone; gravitating said pebbles from said elevator zone through said upper pebble transfer zone to said pebble heating zone; heating said mass of pebbles in said heating zone to a temperature in the range of 12.00 to 2400 F.; introducing a heavy liquid hydrocarbon feed boiling above 500 F. directly into said elevator zone and maintaining a hydrostatic head or liquid level therein such as to force the feed into said reaction zone through said lower pebble transfer zone and maintain a liquid level in said reaction zone; gravitating said pebbles through said reaction zone at a rate such as to continuously vaporize and crack said feed to lighter hydrocarbons; and recovering cracked hydrocarbon product from said reaction zone.

2. The process of claim l in which a plurality of product streams are removed from said reaction zone at different levels above the liquid therein.

3. The process of claim 2 in which an effluent stream in liquid phase is withdrawn from said reaction zone below the liquid level therein.

4. The process of claim 1 in which the gravitation rate of said pebbles through said reaction zone is regulated in a pebble dow control zone in said lower pebble transfer zone and the ilow of feed is bypassed around said zone.

5. The process of claim 1 in which the liquid feed is introduced to the elevator zone at approximately atmospheric temperature.

6. Pebble heater apparatus for the pyroyltic conversion of liquid hydrocarbons comprising in combination a pebble heating chamber having a pebble inlet and gas outlet in its upper section and a gas inlet and a pebble outlet in its lower section; a reaction chamber disposed below said heating chamber, having a pebble inlet and gas outlet in its upper section and a pebble outlet in its bottom; a throat connecting the pebble outlet of said heating chamber with the pebble inlet of said reaction chamber so as to provide for gravitation of pebbles through the chambers; a pebble elevator connected at its lower end with the pebble outlet in said reaction chamber by means of a lower chute sloping downwardly to said elevator and at its upper end with the pebble inlet in said heating chamber by means of an upper chute sloping upwardly to said elevator; a continuous bed of pebbles extending from the pebble inlet in said pebble heating chamber to the pebble outlet from said reaction chamber; a feed inlet line leading into said elevator for introducing liquid feed thereto for flow through said lower chute into said reaction chamber and a liquid level controller in liquid level-sensing communication with said elevator at a level therein corresponding to an upper sec- '6 ing in actuating communication with a flow control valve in said feed line and adapted to maintaining a predetermined liquid level in said reaction chamber in the upper section thereof below the top of the pebble bed therein.

7. The apparatus of claim 6 including a pebble feeder in the chute leading to the lower end of said elevator and a feed bypass line communicating between said reactor and said chute below said feeder adapted for passing hydrocarbon feed around said feeder.

8. The apparatus of claim 6 including a liquid euent line in the side of said reactor below the liquid level therein.

9. The apparatus of claim 6 in which said elevator is of the bucket type having perforate buckets for draining the hydrocarbon feed therefrom and from the pebbles therein.

l0. The apparatus of claim 7 in which the pebble feeder is of the star type having perforate vanes adapted to pass a portion of the feed to the reaction chamber through said feeder.

11. The apparatus of claim 6 including a plurality of product eiuent lines communicating with the upper section of said reaction chamber at different levels above said liquid level.

12. A process which comprises flowing a continuous body of liquid reactant upwardly in a pyrolytic conversion zone countercurrently to a gravitating continuous mass of hot pebbles at a temperature above pyrolytic conversion temperature of said liquid reactant so as to convert same to more desirable products and maintaining a level of said liquid reactant in said mass of pebbles.

13. The process of claim l2 in which said liquid reactant is a hydrocarbon.

14. The process of claim 13 in which said hydrocarbon boils above 500n F.

l5. The process of claim 12 in which the upward ilow of liquid reactant is eected by a hydrostatic head of said liquid in a zone outside said conversion zone.

16. The process of claim l5 in which said pebbles are passed from the bottom of said conversion zone thru a pebble transfer zone to a pebble heating zone above said conversion zone and said hydrostatic head is maintained in said pebble transfer zone.

17. Pebble heater apparatus for the pyrolytic conversion of liquid reactants comprising in combination a pebble heating chamber having a pebble inlet and gas outlet in its upper section and a gas inlet and a pebble outlet in its lower section; a reaction chamber disposed below said heating chamber, having a pebble inlet and gas outlet in its upper section and a pebble outlet in its lower section; a throat connecting the pebble outlet of said heating chamber with the pebble inlet of said reaction chamber so as to provide for gravitation of pebbles through the chambers; a pebble elevator connected at its lower end with the pebble outlet in said reaction chamber by means of a lower chute sloping downwardly to said elevator and at its upper end with the pebble inlet in said heating chamber by means of an upper chute sloping upwardly to said elevator; a pebble feeder in said lower chute for passing pebbles to said elevator from said reaction chamber; a liquid feed inlet line communicating with said elevator downstream, pebblewise, of said pebble feeder for introducing liquid feed to said elevator and means for maintaining a liquid level in said reaction chamber.

18. A process which comprises flowing a continuous body of liquid upwardly in a pebble heat-exchange zone countercurrently to a gravitating mass of hot pebbles at a temperature above the vaporization temperature of said liquid so as to vaporize same; and recovering the resulting vaporous material from said heat-exchange zone.

19. The apparatus of claim 17 wherein said means tion of the pebble bed in said reactor, said controller beu for maintaining a liquid level in said reaction chamber Y7 comprises allow-control valve 'in' said liquid feed inlet line, a liquid-level controller on said elevator at a level eorresponding 'substantially to the desired Yliquid level in said reaction chamber and operatively connected with said flow control valve. y

VEvans et al Ian. 29, 1946 Ferro Dec. 16, 1947 Y 8 f Utterback Y Y Iuly13,y 1948 Ford -..2.2; Oct. 12, Kirkbride (Apr. 3, 1951 Leier Apri. 10, 1951 Hepp et a1. Julv 10, 1951 'BOWleSiet al. July 1951 Quigg'et al Oct. 23, 1951 Weinrich Mar. 4, 1952 Grossman Nov. 4, 1952 

1. A PROCESS FOR CRACKINGG HEAVY LIQUID HYDROCARBON IN CONTACT WITH A HOT GRAVITATING MASS OF PEBBLES WHICH COMPRISES GRAVITATING A COMPACT MASS OF PEBBLES SUCCESSIVELY THROUGH A SERIES OF ENCLOSED CONTIGUOUS ZONES, COMPRISING A PEBBLE HEATING ZONE, A RELATIVELY NARROW CONNECTING ZONE, AND A HYDROCARBON HEATING AND CRACKING ZONE; GRAVITATING SAID PEBBLES FROM THE BOTTOM OF SAID HEATING AND CRACKING ZONE THROUGH AN ENCLOSED LOWER PEBBLE TRANSFER ZONE TO AN ENCLOSED PEBBLE ELEVATOR ZONE; ELEVATING SAID PEBBLES TO AN UPPER ENCLOSED PEBBLE TRANSFER ZONE ABOVE THE UPPER END OF SAID PEBBLE HEATING ZONE; GRAVITATING SAID PEBBLES FROM SAID ELEVATOR ZONE THROUGH SAID UPPER PEBBLE TRANSFER ZONE TO SAID PEBBLE HEATING 